1. Field of the Invention
The present invention relates to a charge controlling circuit, a charge controlling method, and an electronic device provided with the charge controlling circuit and more particularly to the charge controlling circuit being able to be suitably used in a small-sized portable electronic device such as a portable cellular phone, PDA (Personal Digital Assistant), portable music reproducing device, or a like, the charge controlling method, and the electronic device provided with the charge controlling circuit.
The present application claims priority of Japanese Patent Application No. 2004-302763 filed on Oct. 18, 2004, which is hereby incorporated by reference.
2. Description of the Related Art
A portable electronic device, such as a portable cellular phone, is so configured that specified operations are performed by using a secondary battery mounted therein as a power source and, when being powered on, a remaining capacity of the secondary battery is automatically displayed on an indicator on its displaying unit. A user, when recognizing that there is no or little remaining capacity of the secondary battery, attaches a charging device to the electronic device to charge the secondary battery.
Included among the portable electronic device of this kind is a portable cellular phone. The portable cellular phone 1, as shown in FIG. 6, is made up of an upper-side unit 10 and a lower-side unit 20 in which the upper-side unit 10 and the lower-side unit 20 are coupled to each other with a hinge portion 11 interposed between the upper-side unit 10 and the lower-side unit 20. The upper-side unit 10 has an antenna 12, a display portion 13, and a speaker 14 on its front face being put in direct contact with the lower-side unit 20 when the upper-side unit 10 folds in a manner in which the upper-side unit 10 is put in contact with the lower-side unit 20. The lower-side unit 20 has an operating section 21 made up of a plurality of buttons or a like and a microphone 22 on its front face being put in direct contact with the upper-side unit 10 when the lower-side unit 20 folds in a manner in which the lower-side unit 10 is put in contact with the upper-side unit 20. When the secondary battery (not shown) serving as a power source mounted in the portable cellular phone 1 has discharged, the secondary battery is charged again by being put on and connected to a base 30 in which a dedicated charging device is embedded. The base 30 used as the charging device supplies source voltage to be fed from an AC (Alternating Current) adapter 31 to a charging power inputting terminal (not shown) mounted in the lower-side unit 20.
FIG. 7 is a schematic block diagram showing electrical configurations of the AC adapter 31 and of main components making up the portable cellular phone 1 shown in FIG. 6. The portable cellular phone 1 shown in FIG. 7 includes a CPU (Central Processing Unit) 23, a charge controlling IC 24, a resistor 25, and a secondary battery 26. The CPU 23 controls the entire portable cellular phone 1 based on programs so that, in the example in particular, a high (hereinafter referred simply to as “H”) control signal “a” is output while the secondary battery 26 is being charged. The charge controlling IC 24, when the control signal “a” fed by the CPU 23 is high, supplies a charging current set by the resistor 25 to the secondary battery 26 by using power fed from the AC adapter 31. The charging current is controlled by an emitter follower or source follower (not shown) mounted in the charge controlling IC 24. The secondary battery 26 is made up of, for example, a lithium ion battery or a like and is detachable/attachable from or to the portable cellular phone 1. Thus, the CPU 23, charge controlling IC 24, and resistor 25 make up the conventional charge controlling circuit.
The conventional charge controlling circuit is so configured that supply of a charging current is suppressed, by proper setting of a resistance value of the resistor 25, to the degree to which excessive amounts of heat are not liberated in the secondary battery 26 and in the emitter follower or source follower mounted in the charge controlling IC 24 while the secondary battery 26 is being charged. In this case, as shown in FIG. 8, when the charging is started, the secondary battery 26 is put on charge in a CC (Constant Current) charging mode, that is, at a constant current. In the charge controlling IC 24, the current value is made variable by using the external resistor 25. Thereafter, when a voltage of the secondary battery 26 exceeds about 4.1V, the charging mode is switched automatically to a CV (Constant Voltage) mode so that the secondary battery 26 is put on charge at a constant voltage. Then, the voltage of the secondary battery 26 gradually comes near to 4.2V being a fully-charged voltage. The charge controlling IC 24 outputs a voltage of 4.2V and passes a current requested by the secondary battery 26 and, therefore, the current gradually continues to decrease until the charging is completed at time “te”.
Besides the conventional technology employed in the above portable cellular phone 1, another conventional technology of this kind is disclosed in Japanese Utility Model Application No. Hei 01-107875 (recited on page 1 and shown in FIG. 1). That is, in a vehicle storage battery device using the disclosed conventional technology, an overheating preventing element made of a conductive plastic which causes a rise in resistance value as, a temperature increases is inserted into a part of a charging line which feeds a charging current used to charge the storage battery at a constant voltage and is in close contact with a surface of a cell box of the storage battery. This enables suppression of a rise in a charging current occurring at time of the rise in temperature of the storage battery and also prevention of early deterioration of the storage battery.
A battery charging device as the conventional technology of this kind is also disclosed in Japanese Utility Model Application No. Hei 6-24359 (recited in Abstract and shown in FIG. 1) in which a heat sensitive element whose characteristic changes due to a rise in temperature is thermally coupled to a secondary battery and a charging current decreases or is cut off due to a rise in temperature of the secondary battery. This enables overcharge of the secondary battery to be prevented.
Moreover, a charging device as the conventional technology of the above kind is also disclosed in Japanese Patent Application Laid-open No. 2001-314045 (recited in Abstract and shown in FIG. 1) in which an environmental temperature of the charging device and a temperature of a battery are measured and, when the environmental temperature of the charging device and/or the temperature of the battery increase, by decreasing a controlling current value of the charging device and a charging voltage, prevention of overcharge of the battery is made possible.
Furthermore, another charging device having a temperature sensor as the conventional technology of the above kind is also disclosed in Japanese Patent Application Laid-open No. Hei 07-222370 (recited on Page 5 and shown in FIG. 1) in which temperatures of a transistor of a power circuit and/or a heat-liberating component such as a transformer or a like are detected by the temperature sensor so that a charging current of a secondary battery is controlled and, if an error occurs in detection of a fully-charged state, the detection of the full-charge is discontinued so that the secondary battery is charged.
However, the conventional charging circuit as described above has following problems. That is, in the electronic device operating with the secondary battery 26 being mounted such as the portable cellular phone 1, there is a tendency, in recent years, that the secondary battery 26 is so configured that its capacity is increased to satisfy extension of operating time. Therefore, in the case of use of the conventional charging current, since charging time between start of putting the secondary battery 26 on charge and completion of the charging is made longer, it is expected that the charging time is shortened by increasing the charging current. However, the charging current is controlled by an emitter follower or source follower mounted in the charge controlling IC 24 and, therefore, when the charging current is increased, generation of heat in the emitter follower or source follower increases and, as a result, an event occurs that the rise in temperature is brought up to a surface of a main body of the portable cellular phone 1.
Moreover, in the case of a comparatively large-sized electronic device such as a notebook personal computer or a like, measures to diffuse heat or to let the heat escape outside of the main body of the electronic device are taken by using a heat sink, cooling fan, or a like. However, in the case of a small-sized portable electronic device such as a PDA, portable music reproducing device, or a like as well as the above portable cellular phone 1, its cabinet is too small and it is, therefore, impossible to take such positive measures as above from the viewpoint of characteristics of a product itself. Under this circumstance, if charging currents are increased, a user of the portable device suffers a low-temperature burn (so-called cold burn) due to generation of heat in some cases. Therefore, in the case of such small-sized portable devices as above, by decreasing a charging current to the degree to which generation of heat becomes excessive, generation of heat is suppressed. As a result, a problem occurs that, due to a small amount of a charging current, full-charge cannot be achieved unless their batteries are charged for a long time.
Also, a purpose of the vehicle storage battery device disclosed in the Japanese Utility Model Application Laid-open No. Hei 01-107875 is to increase a life of the storage battery and the method is limited to a case where the storage battery is charged by constant-voltage charging. Therefore, this purpose is different from that of the present invention.
Also, a purpose of the battery charging device disclosed in the Japanese Utility Model Application Laid-open No. Hei 06-24359 is to prevent overcharge of a battery by utilizing a characteristic that, when charging of a secondary battery is completed, the secondary battery rises in temperature. Therefore, this purpose is also different from that of the present invention.
Moreover, a purpose of the charging device disclosed in the Japanese Patent Application Laid-open No. 2001-314045 is to prevent overcharge of a battery. Therefore, this purpose is different from that of the present invention.
Furthermore, a purpose of the charging device having a temperature sensor disclosed in the Japanese Patent Application Laid-open No. Hei 07-222370 is to prevent thermal-runaway of a transistor in a power circuit. Therefore, this purpose is different from that of the present invention.